Replaceable valve seats are well known in the prior art. With these valve seats, leak paths exist at both the valve seat seal and the disk seal. When such valve seats leak, it is not possible to determine whether the leak originates in the valve seat seal or the disk seal. As a result, both the valve seat seal and the disk seal must be replaced. Replacement of the valve seat seal is difficult and can result in permanent damage to the valve body. It is desirable to have a positive indication of the leak source to avoid unnecessary repairs.